This invention concerns a water level locking device for water tanks, particularly one used for water tanks installed on top of buildings, for precisely stopping water from flowing in the tank when the water level in a water tank has reached a preset maximum level and allowing water to flow in when the water level falls below a preset minimum level.
A prior art mechanical device for controlling water level in a tank is shown in FIG. 9, and a similar prior art device having electrically-controlled actuation is shown in FIG. 10. The device of FIG. 9 operates by use of a float-coupled lever which positions a cone-shaped stopper to stop water from flowing in to the tank when the float rises with the water to the preset maximum water level. The device of FIG. 10 incorporates with a cone-shaped stopper and a float-coupled lever and electric switch and a meter to control water level.
These types of water level locking devices in the prior art have been found to have the following disadvantages:
1. The water level locking devices employ a cone-shaped stopper which tends to allow water to flow into the tank upon slight displacement of the float, a gap being formed between the stopper and the outlet thereby. Consequently, the tank is often unnecessarily supplied with water, extraneous noise is unnecessarily produced. PA0 2. The devices employ a push rod coupled to the float to directly control stoppage or opening of the outlet. Water tanks installed on high buildings are often supplied with a high-pressure pump means to inject water therein, and the closing pressure applied on the stopper by the water contained in the tank may be insufficient to block the incoming water flow. PA0 3. If an electric water level controller is employed, electric wires must be extended to the roof of a building, adding additional expense and labor to installation and maintenance. PA0 4. Devices which employ a pressure pump include a motor 91, a pressure tank 92, a pressure switch 93, and a stop valve 94. These devices suffer from shortcomings such as noisy operation, short service life of the motor, and the high cost of the pressure tank. PA0 6. Also, in such devices, extra wiring necessary for the electric device that controls water level may increase cost even for installation in residential homes, and may result in unsightly wiring if installation is not performed during construction of the home.
5. In such devices employing a pressure pump, the limit switch for controlling water level is usually turned off to let the motor remain inoperative when water in the water supply is under enough pressure to be forced up to the tanks on top of a given building. Consequently, there are opportunities for the pump leaves and the shaft seals to rust and cease operation. Worse yet, the motor may be impaired when subsequently turned on.